1. Technical Field
This invention relates generally to antenna reflector systems and, more particularly, to a system and method for generating a plurality of beam coverages with a dual-reflector antenna system.
2. Discussion
Communication satellites and the like commonly employ antenna reflector systems for focusing or reflecting signals within beam radiation patterns. Shaped reflectors have been provided, which in combination with a single feed, have been employed to cover a selected shaped beam radiation pattern. For instance, a shaped reflector may be deployed in space to provide adequate coverage throughout a geographic area such as the mainland portion of the United States. However, typical requirements imposed for communication satellites and the like have generally required coverage of the mainland portion of the United States as well as coverage of remote locations such as Hawaii, Puerto Rico and Alaska, for example.
Separate antenna reflector systems have been employed to separately generate each beam pattern coverage. Such systems generally require separate dual-reflector systems for each of the feed horns utilized therewith. This generally results in unnecessary complexity and weight which are undesirable for space-related applications and the like. It is conceivable that a dual-gridded shaped reflector could be used to provide multiple beam coverage to a limited extent. However, dual-gridded shaped reflectors must conform with dual linear polarization specifications. In addition, the dual gridded reflector requires polarization grids which generally results in rather extensive manufacturing requirements and high costs amongst other disadvantages.
More recently, a conventional dual-reflector antenna system exists for providing a main beam coverage in addition to a secondary spot beam coverage. The conventional dual-reflector antenna system generally includes a subreflector that is positioned to communicate with a main reflector. While transmitting, the subreflector is illuminated with a primary energy signal generated by a first feed horn. The primary energy signal is reflected off the subreflector and the main reflector to produce a first or main beam coverage. In addition, the conventional dual-reflector configuration usually employs a second feed horn which is generally positioned beside the main feed horn. The second feed horn likewise illuminates the subreflector with a second energy signal which in turn is reflected from the main reflector to produce a second or secondary spot beam coverage.
While the conventional dual-reflector configuration may serve well for some applications, there are limitations which generally make it unfeasible for space related applications and the like. For instance, the secondary spot beam may be required to cover a much smaller geographic area than the main beam coverage. Due to the difference in the sizes of the main beam and the spot beam coverage, the second feed horn must generally be defocused to get a good performance over the geographic area covered by the spot beam. This generally requires that one of the feed horns be positioned behind the other feed horn, thereby causing a partial blockage of one of the beam paths. In doing so, one of the feed horns is usually positioned within the beam coverage of the other feed horn. As a consequence, the partial blockage exhibited by the conventional dual-reflector configuration degrades the overall performance of the reflector antenna system.
It is therefore desirable to provide for an enhanced dual-reflector antenna system which more effectively generates a secondary spot beam coverage in addition to a main beam coverage. It is further desirable to provide for such a reflector antenna system which generates a plurality of secondary spot beam coverages. In particular, it is desirable to provide for such a multi-beam shaped dual-reflector configuration which does not suffer from feed horn blockage or interference such as that which exists with the aforementioned conventional approach. In addition, it is desirable to provide for a more highly integrated low cost dual-reflector antenna configuration which may be easily manufactured.